1) Field of the Invention
The present invention relates to a technology for deciding a backup communication path in a communication network to take care of one or more failures in the link or the communication nodes.
2) Description of the Related Art
The communication traffics in the backbone networks is dramatically increasing along with upcoming of various new services and demands and wide spreading of the Internet. As a result, large capacity and high speed backbone networks are being designed based on the WDM (Wavelength Division Multiplexing) technique.
The OXC (Optical Cross Connect) and the OADM (Optical Add-Drop Multiplexer) are being developed further for efficient operations by flexible control of mesh type network and sharing of preliminary wavelength, and construction of a new communication infrastructure and introduction of services are expected.
If there is failure in a large capacity WDM network, the damage increase with the number of services being provided by the system. Thus, it is an object to develop a high degree management system capable of enhancing reliability of the network. Particularly, a technique of recovering services at high speed from a link failure or communication node failure by optical layer is made important.
The present inventors are doing research on preplan type failure recovery system which realizes high-speed failure recovery in the WDM network (see “Study on preplan type failure recovery system” Yasuki Fujii, Keiji Miyazaki, Kohhei Iseda, Shingakugihou TM2000-60, pp. 67-72, November 2000). In the preplan type failure recovery system, failure information is sequentially notified from a communication node which has detected the failure to adjacent communication nodes with respect to communication nodes where backup communication path information is previously registered (it is called flooding) so that each communication node set up a communication path in parallel according to the set backup communication path information. Thus, time taken for dynamically searching a backup communication path can be reduced and fast service recovery can be expected.
However, even if the communication path can be switched in parallel, if a longer time is taken until a communication node on the backup communication path receives a failure notification, fast service recovery cannot be realized.
FIG. 24 is a diagram to explain such a preplan type failure recovery system. FIG. 24 explains a network based on an optical path which transmits/receives an optical signal between terminals, particularly a network where the WDM technique is employed to multiplex a plurality of optical signals in an optical fiber and the OXC (Optical Cross Connect) is used for relaying.
FIG. 24 represents a case in which communication is preformed on an active communication path 3 between a communication node 1 and a communication node 2. Each communication node is constructed by an optical cross connect as an optical switch. The communication path 3 has communication nodes 17, 10, 12, and 14. Assuming that a failure 11 occurs between the communication nodes 10 and 12, the downstream communication node 12 detects the failure.
The optical cross connect comprises a function of switching a connection state between a port at an optical signal inputting unit side and a port at an optical signal outputting unit side by adjusting an angle of an incorporated mirror (not shown).
The communication node 12, which has detected the failure, transfers a failure notification message 13 containing failure portion information to a communication node 14, and the communication node 14 further notifies it to an adjacent communication node 15, so that the message is sequentially notified to adjacent communication nodes (flooding).
The communication nodes 15 and 16 on the backup communication path and the communication nodes 14 and 17 that switch the communication path transfer a failure notification message to all the adjacent communication nodes except the communication node that has received it only when the failure notification message is received for the first time. Then, the communication path is switched from the active communication path 3 to a backup communication path 4 according to the previously registered backup communication path information.
The communication nodes 15 and 16 on the backup communication path on the set backup communication path or the communication nodes 14 and 17 that switch the communication path are far away from the failure detected communication node 12 and it takes much time to receive the failure notification message, which largely causes delay of the communication path recovery.
Conventionally, previously searched for is a backup communication path where a time for transferring a failure notification message to all the communication node on the backup communication path from a communication node which has detected the failure does not exceed a give limit time at the time of designing the backup communication path, and the backup communication path is set in each communication node (see Japanese Patent Application Laid-Open No. 2002-281068).
FIG. 25 is a schematic to explain a conventional backup communication path design system. In FIG. 25, it is assumed that communication is performed on an active communication path of communication nodes 20, 22, and 23. For example, a time for transferring a failure notification message from a downstream communication node 22 to each communication node is calculated for a failure 21 between the communication nodes 20 and 22.
A communication node group which is present in an area 29 where the failure notification message can be transferred within the given limit time is used to search for a backup communication path. In the example shown in FIG. 25, since the failure notification message cannot be transferred to the communication nodes 26 and 28 within the limit time, the communication nodes are excluded from the communication node group to be retrieved.
In the MPLS (Multi-Protocol Label Switching) communication network which is a packet transfer technique using a label switching system, when a failure occurs in an active communication path, an upstream communication node in the communication link where the failure has occurred detects the failure occurrence and transmits a failure notification message to the downstream along the active communication path. The switching communication node which has received the failure notification message switches the communication path to the previously registered backup communication path.
FIG. 26 is a schematic of a conventional system of switching to a backup communication path in the MPLS communication network. In FIG. 26, it is assumed that communication is performed on an active communication path 37 made of communication nodes 33, 30, 32, and 34. For example, when a failure 31 occurs between the communication nodes 30 and 32, the upstream communication node 30 where the failure 31 has occurred detects the failure, and transmits a failure notification message to the communication node 33 where a backup communication path 38 is set. The communication node 33 which has received the failure notification message switches the communication path to the backup communication path 38.
Also in this case, the communication node 33 which switches the communication path is far away from the communication node 30 which has detected the failure and it takes much time to receive the failure notification message, which causes delay of the communication path recovery. But, as explained in FIG. 25, a communication node which switches the communication path is selected from the communication node group on the active communication path 37, which does not exceed the given limit time, to set the backup communication path so that the problem can be solved.
However, in the technique explained in Japanese Patent Application Laid-Open No. 2002-281068, it is possible to efficiently set a backup communication path which recovers communication within a required recovery time for a failure which occurs at one portion on a communication path, but there is a problem that the setting is difficult for a plurality of failure portions.
In other words, in the conventional technique, there is a problem that since the backup communication paths which can recover communication within a required recovery time are independently set, respectively, the communication resources are not shared between the set backup communication paths when a plurality of failure portions are assumed so that the backup communication path capable of efficiently utilizing the communication resources is difficult to set.
Therefore, how to design a backup communication path capable of recovering communication within a predetermined recovery time while restricting the communication resources when a plurality of failures are assumed is an important task.